ember-bootstrap-issue-830

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  showModal: false,
});

templates.application.hbs

<button onclick={{action (mut showModal) true}}>set <i>showModal</i> to <i>true</i></button><br>
<BsModal @open={{showModal}}>...</BsModal>

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-bootstrap": "2.8.0"
  }
}